TWITTER'S UK boss has personally apologised to women who have been attacked by "trolls" on the social networking site, vowing to do more to protect people from abuse.

Tony Wang, general manager of Twitter UK, posted a series of tweets today saying abuse was "simply not acceptable".

He wrote: "I personally apologise to the women who have experienced abuse on Twitter and for what they have gone through.

"The abuse they've received is simply not acceptable. It's not acceptable in the real world, and it's not acceptable on Twitter.

"There is more we can and will be doing to protect our users against abuse. That is our commitment."

His messages come as Twitter today clarified its rules on abusive behaviour amid a growing backlash over a series of attacks.

The company has updated its rules to make it clear that abuse will not be tolerated and has put extra staff in place to handle reports of abuse, it said today.

The move comes as Scotland Yard said its e-crime unit is investigating allegations by eight people of abuse on the microblogging site.

There has been growing concern over abuse on the site after three female journalists said they had been the subject of bomb threats, while two received threats of rape.

An online petition calling for Twitter to add a "report abuse" button to tweets has already attracted more than 124,000 signatures.

In a message posted on its blog today, Mr Wang and Twitter's senior director for trust and safety, Del Harvey, said: "It comes down to this: people deserve to feel safe on Twitter."

They said the clarified rules make clear that Twitter will not tolerate abusive behaviour, and an "in-tweet" report button has been added so people can report abusive behaviour directly from a tweet.

"We want people to feel safe on Twitter, and we want the Twitter rules to send a clear message to anyone who thought that such behaviour was, or could ever be, acceptable," they wrote.

They said additional staff are being added to the teams which handle abuse reports, adding: "We are committed to making Twitter a safe place for our users."

The bomb threat tweet was sent to Guardian columnist Hadley Freeman, Independent columnist Grace Dent and Europe editor of Time magazine Catherine Mayer, as well as a number of other women.

In separate incidents, Labour MP Stella Creasy and campaigner Caroline Criado-Perez, who successfully fought for a woman's face to appear on £10 banknotes, were threatened on Twitter with rape. Two arrests have already been made in relation to those threats.

The anonymous Twitter accounts from which the bomb threats originated were suspended, although screen grabs were widely circulated online.

Scotland Yard said an investigation into eight allegations had been launched.

The force said: "Detectives from the Specialist Organised & Economic Crime Command have taken responsibility for the investigations into a number of allegations recently made to the MPS relating to allegations of malicious communication made on the social networking site Twitter.

"The Police Central e-Crime Unit (PCeU), who hold the police national cyber crime remit, is now investigating allegations made by eight people that they have been subject to harassment, malicious communication or bomb threats."

It said the decision was taken to centralise the individual investigations, including three from outside London.

Ms Criado-Perez, 29, said today: "While I'm pleased they're listening, it's taken Twitter a week to come up with this.

"Twitter's 'report abuse' button on the iPhone application goes through to the old reporting form - what we're looking for is an overhaul of the system which sits behind the button.

"The current process is lengthy, complicated and impossible to use if you're under sustained attack like I have been.

"Right now, all the emphasis is on the victim, often under intense pressure, to report rather than for Twitter to track down the perpetrator and stop them.

"I am, of course, pleased that they are taking on new staff. The hard facts are that this will take time, investment and properly trained and paid staff - but it's crucial they get this right."

Steve White, of the Police Federation, said the problem was "unpoliceable" and more needed to be done by social media organisations.

He told BBC Breakfast: "The organisations that run these social media platforms probably need to take a long, hard look, they need to take some responsibility.

"It's much like when you go into a shop - there are prevention measures within shops, whether it be security guards or things locked away that you can't get to, which is going to prevent crime, and I think social media sites need to think long and hard about being able to prevent it from happening in the first place.

"Crime has completely changed. Internet crime and e-crime, including the kind of trolling that we've seen this week, is hugely on the rise. Members of the public don't really understand what to do about it as well, so it goes unreported.

"We can't possibly deal with every single comment that someone doesn't like on these social media platforms, but I think the Government's got to take a long, hard look at resources and have got to understand that there is a changing face of crime in this country, and the police service needs to adapt to that and the resources need to be there to do it."